IVUS examination is a medical modality which makes it possible, from the inside of a blood vessel, to examine the inner side of the blood vessel and its wall. For this purpose an ultrasound unit, which is embodied to transmit ultrasound and to measure an echo of the transmitted ultrasound, can be disposed on the tip of the catheter to be introduced into the blood vessel. Image data for a two-dimensional cross-section of the vessel is then created on the basis of the measured echo. In the cross-section the blood surrounding the catheter, the inner side of the vessel wall and if necessary a further part of the wall itself can be recognized. The IVUS technology is preferably employed in the catheter-based interventional examination of coronary arteries. It offers a doctor the option of obtaining images for the artery wall from inside the vessel, which particularly enables constrictions of the arteries (stenoses) to be detected. The disadvantage of IVUS technology however is that the doctor is only shown a cross-section of the blood vessel very restricted in its location. This makes it difficult for the observer to obtain an overview.
A second modality for examining blood vessels is angiography. In this modality the blood vessels are x-rayed by means of an x-ray device and thus a projection of the vessel (angiogram) is obtained in the form of 2D image data. 2D image data is to be understood here and below as data which describes the individual pixels or picture elements of one or more color intensity values in each case for a gray value or for a color value.
To enable the blood vessels to be better recognized in the projection a contrast medium can be injected into the blood vessels. Projections of the blood vessels, on the basis of which the structure of the vessel can be recognized, can in fact be obtained by means of angiography. It is disadvantageous however that details of individual stenoses are not reproduced for instance with the same high local resolution as is possible by means of IVUS technology. The resolution capabilities of angiographic systems are not sufficient for this purpose.